Electric discharge lamp circuit



March 31, 1942. v 'T w. FR'E'CH" 2,278,256

E EbTR'Ic DISCHARGE LAMP CIRCUIT Fild Jan. 27, 1941 Inventor":

Patented Mar. 31, 1942 ELECTRIC ms cnancn Lamrcmcm'r Theodore W. Frech,Cleveland Heights, Ohio, as-

Signor to-General Electric Company, a corpora tion of New YorkApplication January 21, 1941, Serlal No. 376,090

,4 Claims. (or. 116-124) My invention relates to circuits'for electricdischarge lamps such, for example, as fluorescent lamps. Such lamps of awell known and commonly used form have electrodes which are constructedand arranged to be heated by current flow therethrough before thedischarge in the lamp is started. Because the lamp has a negativetemperature-resistance coefiicient its connection across a source ofcurrent of constant potential is made through a suitable currentcontrolling impedance. The impedance employed may be a resistor but itis preferable in order to avoid unnecessary losses to employ a reactor,or a capacitor, or both. In the latter case, where the net impedance ofthe lamp circuit is to be capacitive, certain difiicult1es have beenexperienced in starting the lamp and in avoiding excessive lampdeterioration. Such difiiculties have been apparent particularly withthe lamp on the leading current circuit of a two circuit unit comprisinga lagging-current circuit and a leadingcurrent circuit both connected tobe supplied from the same source and including similar lamps arrangedfor simultaneous operation. In the copending application of Allen F.Prescott, Serial No. 376,081, filed January 27, 1941, there is disclosedand claimed a circuit by which the abovementioned difliculties may beavoided, the circuit including means for rendering the capacitorineifective until after the lamp has been started. My invention is afurther development of that disclosed and claimed in the aforesaidapplication,

- and it has for its object the provision of an imwill bepointed out inthe appended claims.

In the single figure of the drawing which is a circuit diagramillustrating my invention, I represents an electric discharge lamp ofthe low pressure positive column gaseous discharge type which comprisesa transparent'tubular envelope having a filling of rare gas, or metalvapor, or both. The metal :vapor may, for example, be mercury and if thelamp is of the fluorescent type the inner surface of the envelopemay becoated with a suitable phosphor which will fluoresce when an electricdischarge is passed through the mercury vapor. 'The envelope is providedat its ends with suitable electrodes 2 and 2' which are commonly formedas coils of refractory metal wire such as tungsten coated with asuitable electron emissive materlal. The lamp, if desired, may employindirectly heated electrodes of well known form wherein the wire coilserves merely as a heater for the electrodes.

The lamp is connected to be suppliedfrom'the source 3, which may be a 60cycle, 115 volt alternating current lighting circuit, through theconnections 8 and 5. In one of these connections, as l, I have shown themain control switch 6,

and in the other connection, 5, I have shown the ballast for the lampwhich is represented as comprising the reactor 1 and the capacitor 8,the combined reactance of the reactor and the capacitor being such thatthe current taken by the lamp issubstantially thatior which the lamp isdesigned.

For starting the lamp a starter of any one of various forms may beemployed. In the drawing I have represented a starter 9 of theglowdischarge type of the character of that disclosed and claimed by theBench Patent 2,200,443. The

starter illustrated comprises the two electrodes I0 and II 'of which thelatter comprises a bimetallic element of inverted U-shape having at itsfree end a contact which is normally spaced from the electrode ill butwhich is adapted to engage it when heated by a glow discharge takingplace betweenthe two electrodes. Since the contact of the two electrodesshort circuits the discharge path therebetween, the electrode llimmediately l0 and H are in contact with each other they close a seriescircuit through the two lamp electrodes and the lamp ballast. A heatingcurrent, whose value may be approximately twice that of the normal lampcurrent, flows through the lamp electrodes during that interval which isof the proper length to enable them to become heated to an electronemitting temperature. By the subsequent separation of the starterelectrodes a voltage impulse is applied to the lamp to cause thedischarge therein to start in the well understood manner.

As in the aforesaid capacitor is rendered inefiective .until the lamphas been started by providing the capacitor with a shunt circuit whichis controlled by the switch I having the actuating means IS. The switchPrescott application,

is shown having the contact l6 supported on the free end of a bimetallicarm ll, and the member I is shown as a resistance heater in thermalrelation with the arm IT. The contact 16 normally engages a contact 18and thus closes the shunt circuit about the capacitor 8. As thus fardescribed the apparatus is like that disclosed by I the above-mentionedPrescott application.

It should be mentioned at this point that the thermal switch I4 is smalland of light construction, being preferably mounted in an envelope, suchfor example as' that of the starter 9 but filled with air. Under certainconditions I may electrodes being arranged to become initially employ anevacuated envelope containing a predetermined amount of an inert gas forthe purpose of controlling the dissipation of heat from theheater andhence the speed of operation of the switch. It has been found that undercertain conditions, as for example when a low' wattage heater is used,the contact l6 would stick or freeze to the contact l8, the bimetallicarm l'l, under the influence of the heater l5,,being unable to free theone contact from the other in order to open the shunt circuit. Inaccordance with one feature of my invention I have provided the resistorIS in the circuit which shunts the capacitor and is controlled by theswitch I4. In

apparatus of this characterwhere the capacitor had a value of .05 mi. Ihave obtained very good results using a shunting resistor which had avalue of 8 ohms. The purpose of the resistor in the shuntcircuit is, toproduce a higher time constant of the capacitor-resistor circuit so thatsparking at the switch contacts due to the charging and discharging ofthe capacitor is greatly reduced if not entirely eliminated.

Where the resistance heater I5 is permanently included in the lampcircuit there is obviously a certain constant energy loss at all timesduring the operation of the lamp. In order to reduce this constantenergy loss during the use of the lamp, I have provided the switch itwith the additional contact 20, a front contact, which connects with thelamp circuit at the opposite' end. of the resistance heater to thatconnected with the-switch with the result that hen the arm I! supportingthe switch is heated by the lamp current, the switch first opens theshunt circuit around the capacitor and then closes a shunt circuit aboutthe resistance heater l5. Although the contacts l6 and 2G continuallymake and break contact during the operation oi' the lamp, the resistanceheater being thereby alternately shunted and energized, the movement ofthe contact 16 with respect to the contact 20 is so small that it isinvisible to the naked eye. The spacing of the front and back contacts20 and I8 respectively is such that the amount of inovement of thecontact I6 is very small, the advantage of which is that the time ofreset of the switch'in the event of an interruption in the source ofcurrent supply, is reduced to a low value. I

A further feature of my invention is that the front and back contacts 20and I8 are mounted on bimetallic arms 2| and 22 respectively which armsare constructed to move the contacts supported thereby in response to anincrease in the temperature of the ambient in the same direction as thatin which the arm 81 moves its contact it, As a result of thisconstruction the operation of the switchbecomes substantially heated bycurrent flow through said ballast and starting means, a switch connectedto shunt said capacitor, means responsive to the current in said'connecting means for opening said switch after a predetermined timedelay, and means responsive to the current in said connecting means forsubsequently closing a shunt around said switch opening means;

2. In combination, an electric discharge lamp 'having spaced electrodesadapted to be initially heated by the flow of current therethrough,means for starting the discharge in said lamp, ballast for said lampincluding a capacitor, means for connecting said. lamp and ballasttogether in series to be supplied from a source of current supply, aresistance heater in said connection, a circuit arranged to shunt saidcapacitor, a

' circuit arranged to shunt said heater, and a a thermal switch in saidshunt circuit, a resist ance heater in said connection constructed totake but a small amount of powerfrom the lamp circuit and arranged tocause said switch to open, said switch having a light construction andadapted to be opened by a small actuating force,

' and a resistor in said shunt circuit operative to.

increase the time constant for preventing the sticking together of theswitch contacts.

4. In combination, an electric discharge lamp having spaced electrodesadapted to be initially heated by the flow of current therethrough,means for starting the discharge in said lamp, ballast for said lampincluding a capacitor, means for connecting said lamp and ballasttogether in series to be supplied from a'source of current supply, aresistance heater in said connection, a circuit including a resistorarranged to shunt said capacitor, a circuit arranged to shunt saidheater, a switch comprising a movable contact, a rear contact and afront contact, bimetallic means for moving each of said contacts eacharranged to move the contact associated therewith in the same directionin response to an increase in the temperature of the ambient, saidheater being arranged in thermal relation with the bimetallic movingmeans of said movable contact and said switch being arranged in re- Ispouse to the effect of said heater to open said capacitor shuntingcircuit and subsequently to close said heater shunting circuit.

THEODORE W. FRECH.

